VMware

Memory limit on a VM

Dear redditors, what would be the impact, if any, of setting a 12GB memory limit to a VM that has 32GB of configured ram, 32 GB of consumed ram and 4 to 8GB of active memory?

As a side information, vRops suggests reclaiming 16GB on this VM.

I am not fully confident this will have no impact.

Any advice? Any detail I should pay careful attention to?

Thanks



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2 Comments

  1. Assuming tools are installed, the VM would immediately use some combination of balloon and swap. Based on the info provided, my guess would be quite a bit of swap and severely degraded performance.

    Active memory is not a good counter to use for right sizing. Refer here: https://blogs.vmware.com/vsphere/2013/10/understanding-vsphere-active-memory.html

    That said, I would advise never using memory limits in a production environment unless there’s a billing constraint on it as in the case of a service provider. Just lower the amount of memory allocated to the VM.

  2. As per my understanding, it is almost difficult to answer. Because ESXi Resource management is only aware which pages have been touched. Which is a kind of active memory? Consumed memory is what allocated to the OS but was apparently taken using various resource optimization algorithm e.g. ballooning.

    Limit is not a good approach to solve this problem.

    But to answer your question, when put a limit on VM, VM is not aware of it. It will continue to use 32 GB and start pushing towards that limit. If application/service is not using that much you will not get any calls from the application owner. Over time, one will forget this option and then if someone starts troubleshooting might overlook it.

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